Maho 600E2 - Dynamic following error - Y09

Hi everyone,

I am the owner of a MAHO 600E2, (year 1989), equipped with a toolchanger and an optional 4th axis Indexer. The axes have been switched on this machine, so the Y axis is the horizontal spindle axis.

The machine has been working fine, but I occasionally receive error Y09 (“dynamic following error”, “schleppfehler”). The error can appear at any position along the axis.

I first assumed it was the glass scale so I took it apart and cleaned thoroughly with isopropanol, both scale and reader. Also, checked all connectors and cleaned with electronic spray. However, the error remained.
The error is not consistent, and mostly appears after an hour or so. The machine can be standing still with hydraulics on, but I still get the error after a while. The somewhat unpredictable appearance of the error puzzles me.
The machine can also fault out by “freezing” the Y axis, while still possible to jog the X (horizontal) and Z (vertical) axis.
Turning off the machine clears the error. However, once it has appeared it is easier to recreate upon restart.

Setting machine constant 81 to show the dynamic following error, shows values of +/- 0.001 mm. However, when the Y axis “freezes” it stops at around 0.030 mm.
I assume there is some fault either in the measuring system, the measuring card, the servo drive or the motor. Checked the EXE-platine (impulsformer) by switching input/output between the X and Y axis, but the error still showed up for Y so at least that part is excluded.

I am planning to swap the TDM AC servo drives between the X and Y axes, and perhaps also do the same for the measurement cards since they seem to be the same types.
Does this sound like a reasonable approach?

I would be thankful for any ideas on how to further isolate the problem, or where it could be coming from.

Regards,
Stefan

Dynamic following error is a common problem as Maho's age and the ballscrews wear slightly and there is some difference in what the glass scale sees and the servo tachometer. The "Maho Doctor" here has aways recommended simply turning off the dynamic following error constant (enter "0" as I recall) as the machine will ultimately rely on the info from the glass scales and still be accurate.

Thanks Milacron,
Have tried to turn the following error off, but then the machine will "freeze" the Y axis instead, perhaps because it gets out of the allowed drift window.
To me it seems to be some signal disturbance causing a sudden mismatch between the tacho and the glass scale.
When the machine works normally, the error is down to 0.001mm.

se_jazman said:

Thanks Milacron,
Have tried to turn the following error off, but then the machine will "freeze" the Y axis instead, perhaps because it gets out of the allowed drift window.
To me it seems to be some signal disturbance causing a sudden mismatch between the tacho and the glass scale.
When the machine works normally, the error is down to 0.001mm.

Click to expand...

Strange...turning off the following error always worked for me.

I am having the same problem on my machine, but I get error X04 ( when I use 100% speed). On my Millplus there is a display that shows the actual error, if I am correct that's also the case on the 432. If it is wear the error is way more than the other axis.If it is an electronic problem the error following error seems normal. Widening the error range in the parameters is only a solution if the problem is caused by mechanical wear.
Don't swap the motors, I think that will give other problems.

Kees said:

I am having the same problem on my machine, but I get error X04 ( when I use 100% speed). On my Millplus there is a display that shows the actual error, if I am correct that's also the case on the 432. If it is wear the error is way more than the other axis.If it is an electronic problem the error following error seems normal. Widening the error range in the parameters is only a solution if the problem is caused by mechanical wear.
Don't swap the motors, I think that will give other problems.

Click to expand...

Thanks Kees, does your machine have similar drives and motors (Indramat)?

The strange thing is that the machine can be standing still with just hydraulics on.
Following error is +/- 0.001mm all the time, on all axes.
Then after an hour or so in the very same position, it can suddenly show error Y09 or just freeze the axis, and the following error is then 0.030mm.

Yes my machine has still the Indramat stuff.

On my machine the error comes up by movement, yours at idle.
Hasn't the axis moved on your machine while it should be stay in position?

Kees said:

Yes my machine has still the Indramat stuff.

On my machine the error comes up by movement, yours at idle.
Hasn't the axis moved on your machine while it should be stay in position?

Click to expand...

If I understand how these machines operate they constantly moves the axis also in idle, based on the feedback from the scale, but that is only back and forth +/- 0.001mm or so.
So you're right that it moves also in idle.
But I have not measured if the axis actually moves those 0.030mm when the fault appears, should perhaps do that to see if the axis moves or if only the feedback is changing.

I have seen the Y09 error both in idle and in jog, as well as while running a program.

It shouldn't be moving at idle. A CNC should move to a location and eventually stop trying to move once it has reached the final position within a preset number of encoder counts. That might be +/- 5 encoder counts for example, and 5 encoder counts might be +/- 0.001mm. These numbers are just examples. I'm not sure what a Maho uses for counts per mm.

If the axis is still moving, it is due to poor servo tuning. I.e. the PID tuning is such that the servo motor is still servoing back and forth. You would hear this as vibration perhaps and might see the position fluctuate by +/-0.001mm. This can be tuned out, but you'll want to hire a pro to deal with it.

Does it generate this error regardless of where along the scale it is positioned? Or does it always occur at the same spot (like machine home). That will help you diagnose if the scale or following error is a problem.

Swapping servos or encoder input cards might be informative, but you also have to swap the "personality" modules (the silver plate on front of the Indramat controller), and even then, because each servo it slightly different, you may need to adjust servo paramaters after the swap to tune it. Otherwise, you might actually have a worse problem.

I'm not an expert on this. I've spent time tuning servos on Knee mill CNC conversions, but never a Maho. Just making assumptions on my limited understanding of servo systems and what little I know about Indramat controllers.

Regards,
Mike

Lohmeyer said:

It shouldn't be moving at idle. A CNC should move to a location and eventually stop trying to move once it has reached the final position within a preset number of encoder counts. That might be +/- 5 encoder counts for example, and 5 encoder counts might be +/- 0.001mm. These numbers are just examples. I'm not sure what a Maho uses for counts per mm.

If the axis is still moving, it is due to poor servo tuning. I.e. the PID tuning is such that the servo motor is still servoing back and forth. You would hear this as vibration perhaps and might see the position fluctuate by +/-0.001mm. This can be tuned out, but you'll want to hire a pro to deal with it.

Does it generate this error regardless of where along the scale it is positioned? Or does it always occur at the same spot (like machine home). That will help you diagnose if the scale or following error is a problem.

Swapping servos or encoder input cards might be informative, but you also have to swap the "personality" modules (the silver plate on front of the Indramat controller), and even then, because each servo it slightly different, you may need to adjust servo paramaters after the swap to tune it. Otherwise, you might actually have a worse problem.

I'm not an expert on this. I've spent time tuning servos on Knee mill CNC conversions, but never a Maho. Just making assumptions on my limited understanding of servo systems and what little I know about Indramat controllers.

Regards,
Mike

Click to expand...

Thanks Mike,

The error can appear at any position.
The moving in idle, is just a slow and tiny drift, 0.001mm in about 10 seconds, which the system detects and the servo corrects it back.
This seems to be the case on the X-axis as well, so I assumed it was normal, but perhaps it can be tuned better.

Anyway, I did switch the servo between the X and Y axis, by swapping the cables and connectors (motors and servos are the same models for X and Y).
The machine works, and I didn't have to swap the modules. Actually, No error appeared at all so far (so typical, when you want it to appear...).
I'll keep it like this to see if the error shows up on the X or Y axis. That could at least tell if it is the servo or not.

Regards,
Stefan

Good to know swapping Indramat modules seemed to work OK. I'm curious to know more if the problems continue.

I have Innovative Machine Solutions (IMS) coming in next week to do maintenance on my machine, including checking for issues like drift errors, do a ball bar test, change the fluids, etc. Part of this is to make sure the servo tuning and accuracy parameters are all good. I have on rare occasion had my MH1200C fail with following errors like you are experiencing, but in my case, they have always been due to a commanded rapid move. Cleaning the scales helped when I first got the machine, and in general I believe the issues have been due to the machine sitting mostly unused for too long. Anyway, I've learned a lot about Mahos the last few years, but looking forward to having IMS help me out as they do a lot of Maho maintenance and are becoming experts on these older machines as well as all their work on newer stuff of course.

Regards,
Mike